| Current Conditions | ||
| Temp |  | 2.2 C |
| RH | | 22 % |
| Wind | | N 19 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 604 FXHW60 PHFO 200634 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 834 PM HST Fri Jul 19 2019 .SYNOPSIS... A high pressure ridge will remain north of the Hawaiian Islands into the middle of next week. Expect moderate to breezy trade winds through the period with showers favoring windward and mountain areas. Additional moisture may move up from the deep tropics from Sunday into Tuesday, possibly increasing showers across the state for the first half of next week. More typical trade wind weather returns from Wednesday onward. && .DISCUSSION... A more typical trade wind weather pattern continues to unfold with a high pressure ridge north of the islands into the first half of next week. Regional satellite infra-red imagery shows a fairly active Inter Tropical Convergence Zone around 10 degrees north latitude south of the state. Cloud bands with embedded showers are slowly drifting in with the trade winds. In the upper levels of the atmosphere a deep upper low appears on on satellite water vapor imagery. Large scale lift and instability associated with this upper low continues to weaken the stable subsidence inversion over the islands allowing deeper clouds to form and more shower activity mainly along windward and mountain slopes in the overnight through early morning hours through Sunday. Brief periods of showers are possibly over leeward slopes with stronger shower bands moving in with the trade winds. Global models continue to show a weak trough developing south of the Big Island this weekend. Both the American (GFS) model and the European (ECMWF) model are moving this trough in a general westward after it forms. The GFS model has a more northwesterly track, which would result in advecting deeper tropical moisture into the islands for the first few days of next week. The latest GFS model run brings this deeper moisture and enhanced showers into the southern slopes of the Big Island on Sunday night, pushing northward into the island of Maui by Monday afternoon. Meanwhile the ECMWF keeps us in a drier air mass solution with the deep tropical moisture passing well south of the state. We are keeping a close watch on these model differences and are blending both solutions to produce our current medium range rainfall forecast grids. Confidence in enhanced showers for the eastern half of the state remains fair at this time. More typical easterly trade wind weather returns from Wednesday onward with passing shower bands in the easterly wind flow. && .AVIATION... Strong high pressure far northeast of the Main Hawaiian Island will continue to drive mostly dry trade wind flow over the area. Bands of low-topped stratocumulus embedded in the trade wind flow will impact mainly east and northeast facing slopes and coasts. Shower activity will be limited, but is expected to increase overnight. AIRMET Sierra for mountain obscuration has been dropped, but could become necessary again towards morning. Light to locally strong east winds will continue into Saturday and likely beyond. AIRMET TANGO will remain in effect for moderate turbulence below 7,000 ft. && .MARINE... Fresh to locally strong easterly trades are forecast to continue through next week as high pressure remains positioned north-northeast of the area. The stronger winds will remain across the typically windier locations from Maui County to the Big Island due to terrain accelerations. The current Small Craft Advisory remains in place for these areas through Sunday and may need to be extended into early next week. Rough surf will continue along east facing shores each day due to strong onshore winds. Heights are forecast to slightly trend down through the latter half of the weekend into early next week due to the upstream trades trending down. Surf along south facing shores will remain small through the weekend, then trend up through the first half of the upcoming week due to a recent system passing through/near the Tasman Sea. Heights should remain below advisory levels as this south- southwest swell moves through and peaks Monday through Tuesday. In addition to this long-period source, a moderate period small southeast swell is expected through this time. See the latest Oahu Surf Discussion (SRDHFO) for additional details on surf and swell. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Bohlin AVIATION...Bedal MARINE...Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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